Slow Light = Fast Computing

yohaas writes "The Washington Post is reporting that scientists have been able to slow the speed of light while still maintaining its ability to transmit information. The researchers have even developed a way to 'tune' the process, modulating how fast or slow the light goes within controlled circumstances. From the article: 'Scientists said yesterday that they had achieved a long-sought goal of slowing waves of light to a relatively leisurely pace and using those harnessed pulses to store an image. Physicists said the new approach to taming light could hasten the arrival of a futuristic era in which computers and other devices will process information on optical beams instead of with electricity, which for all its spark is still cumbersome compared with light.'"

Comments

Re:*cough*bullsheet*cough*

[ThanatosMinor]

Perhaps they meant only one photon at a time. The interference pattern that light creates on a screen does not depend on whether you send one photon through at a time or an entire beam.

Re:*cough*bullsheet*cough*

[julesh]

There's no way a single photon makes a stencil image.

There's a well-known effect that when you perform Young's double-slit experiment with single photons, the interference patterns still remain. If a single photon can interfere with itself, I'm sure it can make an image.

Re:IBM

[julesh]

The key difference is that IBM's approach didn't actually slow the light down, but rather channeled it through rather long conduits. You couldn't store an image that way, because the light was constrained to move in a single dimension inside a cavity. This can store images, because it is completely three dimensional.

A much better scientific description here

[viking80]

Here is a half decade old article that describes the process well. It also uses units such as nm and Kelvin instead of thigs like "seven times around the earth" and "about 450 degrees below zero"

http://www.physics.hku.hk/~tboyce/sf/topics/lightf reeze/lightfreeze.html

Re:Moo

[exp(pi*sqrt(163))]

The latter article is about phase velocity. Phase velocity is the speed at which the individual peaks and valleys of the signal appear to travel. But peaks and valleys aren't actual 'things' and you can't transmit information using them. (See here.) This latest story is about the rate at which you can transmit information, so it's about group velocity.

Despite the fact that the theory was worked out more well over a century ago, almost every modern pop science story about manipulating the speed of light leaves out these crucial points.

slowing down the speed of light

[ajs318]

It's been done already. Light slows down whenever it passes through anything. It only manages to get up to 299 792 458 ms-1 in a perfect vacuum. Even air slows it a little bit.

Whenever a beam of light moves from one medium, eg. air, to another, eg. glass, its speed changes. If it enters on the skew, so the speed of one side of the beam changes before the other side, then the beam changes direction; just like a vehicle with a binding brake, it swings towards the side that slows down first. When it comes out of the glass back into air, it speeds up again and changes direction again, exactly the reverse way to what would have happened on the way in (since a beam of light always follows the same path, whichever end it's shining from); unless it's travelling at such an angle there's no way it could ever have got to be travelling in that direction by going through the surface and slowing down a bit sooner on one side than the other. In which case it simply bounces off like a pool ball hitting the cushion and tries to escape somewhere else. This is how fibre optics work.

It also means that when you blast a pulse of light into one end of a long fibre optic, some of it comes straight along the middle and out of the other end at the speed of light in whatever stuff the fibre is made out of; but some of it takes a longer journey, bouncing off the walls, and some of it bounces more times than others. So you get a longer pulse at the far end than you originally put in (and dimmer, since the same amount of energy is now being spread over more time). If you're sending many pulses at a high enough frequency, there comes a point when the first pulse hasn't finished arriving at the far end before the second pulse goes in, and the receiver won't be able to tell which is which. Also, if the fibre goes through a bend, sometimes some light that you thought was going to bounce off the walls actually strikes at such an angle as it can get out. With modern, highly flexible materials, this can actually happen without you bending the fibre enough to break it.

If you want maximum bandwidth out of your fibre, you have to take these phenomena into account. You can buy cheap acrylic fibre, with LEDs and phototransistors that screw-couple onto it; these can often be used for RS232 links with no additional components, using the transmitter to light the LED and the phototransistor to pull down the voltage at the receiver, but you'll be lucky to get more than 9600 baud through such a link. With just some simple signal conditioning, you can make it run much faster.

Re:*cough*bullsheet*cough*

[WorseThanNormal]

I don't know why you say this. Unless you're thinking that a photon is a particle and concieving of that particle as a speck of dust of grain of sand. Photons, like electrons, don't always act like a particles. Sometimes they act like waves.

Re:*cough*bullsheet*cough*

[mhall119]

Yes, but when they contact something, the act like a particle. Even in a dual slit experiment, a single photon will produce only a single contact, not a pattern. The pattern arises from the non-uniform distribution of multiple single photon contacts. The original comment's confusion was thinking that the hologram was produced by a single photon, rather than a succession of individual photons.